- Group of objects are handled using collection framework.
- It allows different type of collections (dynamic arryas, Linked List, Trees and hash tables) to work in a similar manner with interoperability.
- Some partial implementations are provided to create own collection.
- Several implementations (such as LinkedList, HashSet and TreeSet) are provided to use.
- Mechanisms were added that allow the integration of standard arrays into the collection framework.
- A interface Iterator is created by collection framework which provides a means of enumerating the contents of collection.
- Since each collection implements Iterator, the elements of collection class can be accessed through the methods defined by Iterator.
- In addition to collections, the framework defines several Map interfaces and classes.
- Maps store key/value pairs.
- Maps are not collection but a collection-view of a map can be obtained and thus contents of a map can be accessed as collection.
The collection framework defines following Interfaces:
- Collection Top of the collection hierarchy.
- List Extends Collection to handle sequnces (lists of objects)
- Set Extends Collection to handle sets (contain unique elements)
- SortedSet Extends Set to handle sorted sets.
- Collections that supports the methods which enable to modify the contents of it are called modifiable otherwise unmodifiable.
- If such method is applied to unmodifiable collection, an UnsupportedOperationException is thrown.
- All the build-in collections are modifiable.
- If a collection can't be modified then UnsupportedOperationException is thrown and a ClassCastException is generated when one object is incompatible object to a collection.